Uncertainty.
Nature, volume 400
“Edwin Hubble got it wrong by an order of magnitude, but claimed an uncertainty of 10%. Seventy years and much humble pie later, knowledge of the constant rate of expansion of the Universe…….. Remained unreliable…
“Had the expansion of the universe proceeded unchanged at the galloping rate suggested by Hubble, the big bang would have taken place less than two billion years ago, making the Earth older than the Universe”